Is the tap water consumed by Shenzhen people absolutely safe?
The pass rate announced by the water affairs department conflicts with the inspection result data of the Centers for Disease Control and Prevention; The by-products produced by chlorine disinfection may be harmful, and this problem also exists in other big cities; The Shenzhen water affairs department announced more than ten years ago Mastering safer new technologies, but not promoting them throughout the city
Wang Hengjia
Jingbao In-depth Investigation Department reporter Wang Hengjia
August 21, 2012, Shenzhen Water Affairs Network announced the city's water quality testing center's full analysis and testing of factory water in July. There are as many as 103 relevant standards. The test results believe that all factory water in Shenzhen districts meets the standards.
After the new "Drinking Water Hygienic Standards" began to be implemented nationwide on July 1, 2012, Shenzhen Water Group announced in a high-profile manner that Shenzhen "passed all project tests in 2007." "Affiliated water plants The passing rate of the new national standard for factory water quality is all 100. “Some indicators are far better than the new national standard indicator limit.”
Relevant people from Shenzhen Water Group said to many media: People feel that the water quality is not good. Many of them are caused by the aging of the pipe network...
Correspondingly, many industry insiders broke the news to Jingbao reporters: 1. A certain national department recently came to Shenzhen to investigate, and several water companies in Shenzhen One of the factory's projects exceeded the standard and was "interviewed" and ordered to make rectifications; 2. The water quality reports published by the Shenzhen Water Affairs Department for many years have problems such as unreliable data; 3. The disinfection technology used by many water plants in Shenzhen will produce disinfection by-products "trihalogens" "Methane", etc., accumulation to a certain extent may cause serious harm to the human body.
The first of the three revelations in the appeal has not been confirmed due to various reasons. The latter two were investigated by Jingbao reporters and found to be based on certain facts...
Relevant investigations show : Disinfection by-products "exceed the standard"
The "Urban Water Supply Water Quality Bulletin" published by the Shenzhen Water Affairs Department on a monthly basis from 2007 to the present basically declares that "the passing rate of factory water samples is 100%." However, surveys conducted by other professional organizations suggest otherwise.
From 2007 to 2009, experts from the Shenzhen Municipal and District Centers for Disease Control and Prevention conducted three surveys. The inspection showed that the passing rate of municipal water supply factory water samples was 82.9, 84.93, and 85. 0.
In these three surveys, in addition to various conventional data, a very similar issue was also mentioned: disinfection by-products, which were mentioned twice as "exceeding standards" and three times as "higher than other cities." ". This issue is quite unfamiliar to most citizens.
"Actually, this water is considered good in the country."
So, what are the by-products of disinfection? A reporter from Jingbao interviewed Huang Junli, an authoritative expert on tap water disinfection in China and a professor and doctoral supervisor at Harbin Institute of Technology.
Huang Junli said that when the "raw water" used in the water plant is relatively clean, there is no problem with chlorine disinfection. However, if the raw water is contaminated with some organic matter, various disinfection by-products will be produced: Three Halogens, MX, etc. Although the content of these by-products is not very large, most of them are "mutagenic", that is, when they reach a certain concentration or accumulate in the human body to a certain extent, they may cause mutagenesis, carcinogenesis, and deformation.
So, are the disinfection by-products in Shenzhen’s tap water harmful to the human body? Huang Junli said that if the "mutagenicity" is positive, there is the possibility of carcinogenesis and deformation, and the degree of possibility or harm needs further testing to determine.
Between May and June 2008, several experts from the Shenzhen Center for Disease Control and Prevention studied the "genotoxicity" of water from six water plants using "Dongjiang water" and "reservoir water". The "Salmonella typhimurium mutagenicity test", "micronucleus test" and "microfluctuation test" were used to detect and compare the mutagenicity of organic matter in each water sample. The conclusion is that "the organic compounds in the water from the six water plants have obvious mutagenic effects, and frameshift mutations are the main ones; the results of the micronucleus experiment and the Ames experiment on the genotoxicity detection and evaluation of organic compounds in the water are basically consistent."
This study was written as a paper and published in an academic journal, and was corroborated by other papers published around 2010. The conclusion was that the "mutagenicity" of the factory water was positive.
The reporter contacted one of several experts. She confirmed that the six water plants studied were all from Shenzhen, and then said: "This issue is very sensitive. Everyone is drinking this water. If you do this, it will be very troublesome for water plants. In fact, the water we conducted on animals has indeed produced results, but we need to conduct epidemiological investigations to determine the extent of its impact on humans. "Many animals are more sensitive than people, and there are still differences between people and animals." After thinking about it for a few days, she refused to be interviewed in person.
Jingbao reporter interviewed a researcher from the Institute of Environment of the Chinese Center for Disease Control and Prevention. The researcher had conducted tap water surveys nationwide and visited Shenzhen many times. The researcher said that in order to speak freely, he must remain anonymous. His pseudonym is Researcher Pi. Researcher Pi's opinion is the same as that of Huang Junli: any mutagenicity test that is positive may cause harm to the human body. Moreover, several large cities across the country now focus on chlorine disinfection, and have more or less similar problems.
Huang Junli feels suspicious about the data of trihalogenated substances detected by the Shenzhen Water Affairs Department Monitoring Center. He said that he had learned that the Shenzhen Water Affairs Department used the "headspace method" to increase temperature and other conditions to "let the trihalogenated compounds in the water run to the liquid surface, and the liquid level is very large." This method of measurement is inaccurate. To measure accurately, liquid-liquid extraction must be used. For example, Huang Junli said that he himself had conducted experiments. Water samples that could not be detected by the "headspace method" and had no problems at all were detected by the liquid-liquid extraction method but exceeded the national standard.
Researcher Pi said that currently, the country has formulated relevant standards for disinfection by-products such as trihalomethanes, but this does not mean that as long as they are qualified, they are absolutely harmless. Disinfection by-products are lower than relevant standards, causing It is not uncommon to test positive for mutagenicity, and the country currently does not mandate mutagenicity testing. "In order to keep their jobs, leaders of water affairs departments in various places do more things than less things. If they can't do it, they won't do it."
Can the tap water from the six factories involved in the paper fail the food safety evaluation process?
Although the country does not have relevant testing standards and procedures for mutagenicity testing in tap water, it does in food safety.
The "Food Safety Toxicology Evaluation Procedure" (GB15193.1-2003) that is currently being implemented stipulates that the evaluation test is divided into four stages. The second stage is the genetic toxicity test. The relevant regulations are: : "Choose one from the Ames test or V79/HGPRT gene mutation test; bone marrow cell micronucleus test or mammalian bone marrow cell chromosome aberration test; mouse sperm abnormality analysis or testicular chromosome aberration analysis... Among the three tests, If one or more tests are positive in vivo and in vitro, it means that the test substance is likely to have genotoxicity or carcinogenic effects. Generally, the test substance should be abandoned for use in food. If one or two of the three tests are positive in vivo. If one in vitro test is positive, then two more alternative tests (at least one of which is an in vivo test) will be selected. If the additional tests are negative, the next step of the toxicity test can be continued..."
After the revision, the "Food Safety Toxicology Evaluation Procedure" (Draft for Comments), which has not yet been officially promulgated, stipulates that "if two or more tests in the genotoxicity test combination are positive, it means that the test substance is likely to be genotoxic and genotoxic." Carcinogenicity, the test substance should generally be abandoned for use in food."
The above-mentioned two tests, the "Ames test" and the "micronucleus test", were conducted on the water produced by six water plants. , the results were all positive. In other words, if the factory water used in the test is used as food, it is very likely that it will not even pass the second stage safety test, and it will be even more difficult to pass the third and fourth stage tests and be put on the market.
So, is there any way to solve the problem of disinfection by-products?
Huang Junli said that he has a good understanding of tap water disinfection in Shenzhen. As far as he knows, the chlorine dioxide disinfection in some water plants in Shenzhen is not chlorine dioxide disinfection in the true sense, but the real chlorine dioxide disinfection. Chlorine disinfection can solve the problem of disinfection by-products.
Huang Junli said that 80% of water plants in Europe are currently using chlorine dioxide. This disinfectant is very safe.
The reason why some manufacturers in Shenzhen that use chlorine dioxide for disinfection still appear "positive" is probably because the chlorine dioxide hair growth technology they use is a "composite method", which produces chlorine dioxide. While chlorine is produced, a large amount of chlorine gas is produced. It was chlorine gas, not chlorine dioxide, that ultimately caused the positive. Huang Junli said that my country's relevant standards are currently being prepared. Once promulgated, the "composite chlorine dioxide generator" will be renamed "chlorine dioxide and chlorine mixed generator".
Researcher Pi said that based on his own research, “The ratio of chlorine dioxide and chlorine gas produced by the composite chlorine dioxide generator is 1:1 in theory, but in reality it is 1:2, that is, It is said that chlorine dioxide is only 33.”
Researcher Huang Junli and Pi’s statement can also be supported by internal data from Shenzhen Water Group.
Huang Junli said that the chlorine dioxide concentration produced by a real chlorine dioxide generator is above 95. He has used this generator to conduct several years of experiments with different water qualities in many places. The results showed that the "mutagenicity" of the water produced from the factory was negative.
So, when using chlorine dioxide as a disinfectant, will it also produce some disinfection by-products? Huang Junli said that chlorite and chlorate will be produced. When the water quality is not particularly dirty, the amount of pure chlorine dioxide added is only 0.2 mg-0.5 mg/L. Even if all the chlorine dioxide reacts, it will not exceed the national standard. This content has been found to be harmless in repeated tests.
Researcher Pi believes that in a few cases, the dosage of chlorine dioxide may still exceed 1 mg/L. However, even if it exceeds the national standard, chlorite and chlorate are very easy to remove, and simple follow-up processes can be added. The disinfection by-products of chlorine, such as trihalomethanes, are very difficult to remove. Of course, they can also be removed through advanced treatment such as activated carbon, but the cost will be higher, and generally no water plants use them on a large scale.
So, do the experts from the Shenzhen Water Affairs Department know the difference between chlorine dioxide and chlorine disinfection? A reporter from Jingbao found out that as early as 12 years ago, the Shenzhen Water Affairs Department had conducted a special study on this issue.
Shenzhen found a solution to the problem of disinfection by-products as early as 2001
The reporter found a book in the library: "Drinking Water Chlorine Dioxide Purification Technology", published in January 2003. The chief editor of the book is Zhang Jinsong, who is currently the chief engineer of Shenzhen Water Group, and the first editor is You Zuoliang, who is currently the director of the Technology Research Institute of Shenzhen Water Group. The reporter contacted Zhang Jinsong and expressed the hope of interviewing him. He initially agreed, but later said that he needed approval from the group.
The preface of the book states that “Since the discovery that chlorine disinfection can lead to the production of trihalomethanes, haloacetic acids and other ‘trihalo’ compounds, the by-products and products produced by disinfection of chlorine and chlorine derivatives have Its harm has increasingly aroused people's concerns." The book also lists research from the United States and other countries to describe the harm of these by-products to the human body.
The preface also says that "in developed countries, the application of chlorine dioxide in drinking water purification has been very common." ''s scientific research project is jointly undertaken by Shenzhen Water Affairs Bureau and Shenzhen Water Affairs (Group) Co., Ltd., and the project has passed expert acceptance in December 2001."
Page 10 of the book says “Chlorine dioxide has strong selective oxidation ability and broad-spectrum high-efficiency sterilization ability. It produces almost no organic by-products of chlorine disinfection during the water purification process...Chlorine dioxide has It is produced and used in drinking water purification in many countries and has become one of the best alternative disinfectants to chlorine."
So, what is the difference between pure chlorine dioxide generator and "composite chlorine dioxide generator". Difference, have they studied it?
On page 244 of the book, when studying a water plant in Shenzhen that uses a "composite method chlorine dioxide generator", it is written that "the composition analysis of the chlorine dioxide mixture produced by the generator (before entering the raw water) shows that , the percentage of chlorine is slightly higher than that of chlorine dioxide.
"Page 262 of the book reads, "Chlorine dioxide generators are divided into two categories: one is chlorine dioxide disinfectant generator, the other is chlorine dioxide compound disinfectant generator... Chlorine dioxide disinfectant generates Device...the total score is not less than 95. ”
Do they know that the factory water is positive for mutagenicity?
The two tables listed on page 244 of the book are for water disinfected with chlorine in Shenzhen. The results of the "Ames test" of a water plant using a "composite method chlorine dioxide generator" for disinfection were all positive.
The book also analyzes that even if "composite method chlorine dioxide generator" is used for disinfection, the "Ames test" results are positive. There is a large amount of chlorine in the disinfectant produced by the "disinfectant" which affects the test results, but the "mutagenicity of drinking water" is "still lower" compared with water plants that purely use chlorine for disinfection.
Then, What are Shenzhen's water plants using for disinfection now? The description at the end of the "Urban Water Supply Water Quality Bulletin for June 2012" released by the Shenzhen Water Affairs Network said that "water samples with * indicate chlorine dioxide disinfection method." The reporter counted the Of the 46 water plants announced, 13 have the "*" mark, and of these 13, according to insiders, many use "composite chlorine dioxide generators", and the remaining 33 are said by industry insiders. Except for a few that use ozone for disinfection, experts believe that cost and interest conflicts have led to most water plants not using chlorine dioxide.
Why have we already recognized the benefits of pure chlorine dioxide but have not used it yet?
The answers given by researcher Huang Junli and Pi include three answers: 1. Habit; 2. Cost; 3. Interest disputes. . They said that this is not a problem in Shenzhen alone. Similar problems exist in big cities such as Beijing, Shanghai and Guangzhou.
Huang Junli said that many water plant leaders have the impression that chlorine dioxide is expensive and the technology is troublesome; chlorine is cheap. , and it has been used for many years. In fact, at present, based on the calculation of 0.5 mg/L of chlorine dioxide and 2 mg/L of chlorine, the cost of chlorine dioxide disinfection per liter of water is only less than 0.5 cents. mg/L may even be cheaper, and the technology is easy to learn.
Huang Junli said that several manufacturers that previously produced "composite chlorine dioxide generators" made a lot of money and were very wealthy. There are interests in equipment maintenance, and there is resistance to replacing them with pure chlorine dioxide generators.
Researcher Pi said that our country's chlorine dioxide disinfection technology has been promoted in water plants below the county level. Very good, some areas have reached over 90. Large cities such as Beijing, Shanghai and Guangzhou used to basically use chlorine. Before the 2008 Olympics, Beijing felt that chlorine was dangerous and could explode, and it was troublesome to train personnel with chlorine dioxide, so it switched to sodium hypochlorite, which does not It exploded, but the disinfection byproducts remained. Beijing used it, and some places in Shanghai followed suit and used sodium hypochlorite.
As for the reason why chlorine dioxide is easy to promote in small places but difficult to use in big cities, researcher Pi believes: First, because big cities have traditions, some leaders are afraid of making mistakes by changing traditions; second, because small cities are far away from industrial centers and it is inconvenient to buy liquid chlorine. Big cities can get cheap liquid chlorine and have a fixed supply for a long time. The annual supply volume is very large, and there is a conflict of interest, which is difficult to break.
The facts involved in a previous report by Jingbao can illustrate some problems: Pingshan Water Company bought carbon dioxide. For chlorine generators, the family members of the leader of the water company later established a company to produce chlorine dioxide generators and sold them to several surrounding water companies at high prices for use. Later, some manufacturers suspected that they were counterfeiting their own patented products, so they sued. As a result, it is said that all chlorine dioxide generators were discarded and reused for chlorine disinfection.
The book "Drinking Water Chlorine Dioxide Purification Technology" edited by Zhang Jinsong has the following statement: "Since the vast majority of water sources in our country are in a slightly polluted state, when chlorine dioxide is used for disinfection, its investment The dosage is generally above 0.5 mg/L... The concentration of chlorite has exceeded the standard... When chlorine dioxide is used for pre-oxidation, the dosage is generally around 2 mg/L... A water plant in Shenzhen... Chlorite The acid salt exceeds the standard by 0.5-2 times... According to the current drinking water hygiene standards, an important issue in using chlorine dioxide for purification is to solve the problem of chlorite by-products in the water.
However, adding new process measures will inevitably increase new investment and operating costs, which undoubtedly reduces the application value of chlorine dioxide, which is slightly more economical than chlorine. ”
The book believes that “the water purification cost of the most expensive liquid stable chlorine dioxide is nearly 7 times that of chlorine. Even the lowest cost... its cost is 24 times higher than that of chlorine.” "
After 2002, Zhang Jinsong and You Zuoliang also published many papers discussing the control and removal of chlorite and chlorate, the disinfection by-products of chlorine dioxide. One article stated that " The concentration of chlorate produced during the drinking water purification process will not be very high, and its harm will not become a big problem, and it should gradually fade out of drinking water control standards. Another article proposed a process solution: "The chlorite concentration may exceed the standard... The ferrous salt reduction method is a more environmentally friendly and technically and economically feasible method." ”
Researcher Pi analyzed the psychology of many water workers and said, “The use of chlorine dioxide is inherently expensive. If the water pollution is serious, the investment will be even more expensive. After the investment is increased, follow-up will be required.” Only by treating chlorite can the standard not be exceeded. Although subsequent treatment is cheap, it also costs money. Using chlorine can save money. Although some disinfection by-products are produced, it is not easy to exceed the standard. Even if the standard is exceeded, it can be 'not exceeded' by changing the detection method. As long as the test result does not exceed the standard, as for whether the test result is 'positive', since the country does not have mandatory testing, it can be ignored. ”
Fifteen years ago, direct drinking water in a village in Meilin became “absolutely safe”
The book "Chlorine Dioxide Purification Technology for Drinking Water" mentioned that as early as 1998, Meilin Village has used ozone activated carbon ultrafiltration chlorine dioxide treatment technology, and the water can be drank directly.
Today, the city’s factory water still does not publish the results of the “Ames test”, but 15 years ago, Meilin. However, one village did a test and the result was negative. The chlorine dioxide generator used by Meilin Village was an imported BELLOZON generator. This generator imported 15 years ago was not the "compound method" used by many water plants in Shenzhen. "Chlorine dioxide generator", but "pure chlorine dioxide generator". "Drinking Water Chlorine Dioxide Purification Technology" said that the disinfection cost of piped direct drinking water in Meilin Village reaches 0.497 yuan/cubic meter.
Researcher Pi said that the water treated by these procedures is one of the most absolutely safe in the world. This also shows that "Shenzhen water personnel already knew what to do", but they did not solve the problem of "for whom".
What should citizens do if they are worried about the water they drink? Some papers believe that if the water is boiled for 5 minutes, the chlorine disinfection by-products will be reduced to a low point.
Researcher Pi. Said: First of all, the water from some water plants in Shenzhen, such as the Bijiashan Water Plant that supplies water to the central area, is still very safe, because even with chlorine, disinfection by-products can be removed through post-processing, but the cost is higher. Shenzhen uses water with related technologies. There are very few factories. Secondly, citizens don’t need to be too afraid, because there is a process of accumulation of harmful effects, and there is also a risk of illness. Finally, if you attach great importance to healthy treated water, if there is advanced treatment in the future, you will have to increase your living costs to purchase purified water in the short term. When purchasing equipment, do not believe the false propaganda of some manufacturers. The equipment does not need to be expensive. The most critical devices are two: ultrafiltration and activated carbon. If you are only worried about disinfection by-products, activated carbon is enough. /p>
Data
100
Data released by Shenzhen Water Affairs Network
May and December 2008, July and December 2009" "Urban Water Supply Water Quality Bulletin" all stated that in accordance with the "Hygienic Standards for Living Drinking Water" (GB 5749-2006), the passing rate of factory water in that month was 100. In the past few months, the factory water from 40, 43, 44, and 45 water plants were tested respectively. .
82.9
Survey by experts from the Municipal and District Centers for Disease Control and Prevention
Among the 106 indicators tested, some water plants have turbidity, aluminum , manganese and residual chlorine are unqualified.
The concentrations of disinfection by-products in Shenzhen municipal factory water are lower than the national standard, but higher than other cities...chlorite, chlorate, trichloroacetaldehyde, carbon tetrachloride and trichloride The methane concentration is relatively high, reaching more than 10 of the limit... Attention should be paid to the control of disinfection by-products.
(In May 2008, experts from the Shenzhen Municipal and District Centers for Disease Control and Prevention collected factory water samples from 35 water plants in Shenzhen (accounting for 72.9% of all water plants) for research. Water quality inspection and The results are evaluated in accordance with the "Standard Test Methods for Drinking Water" (GB/T 5750-2006) and "Hygienic Standards for Drinking Water" (GB 5749-2006).
Municipal and district disease prevention and control. Center expert survey
84.93
There were 14 items among the 73 water samples, and 11 water samples were unqualified. The main unqualified water quality indicators are still conventional indicators, such as aluminum, Turbidity, manganese, free residual chlorine and chlorate, etc.; "In 2 water samples, the sum of the ratios of the actual measured concentrations of chloroform, chlorodibromomethane, dichloromonobromomethane, and bromoform to their respective limit values ??exceeded 1, Therefore, these two water samples were judged to have exceeded the standard for trihalomethanes; compared with other cities, the concentration of disinfection by-products in Shenzhen's municipal factory water was higher than in other cities.
(September 2007 (rainy season) and In May 2008 (dry season), 35 municipal water plants were selected for monitoring)
Expert survey from the Municipal Center for Disease Control and Prevention
85
Mainly not. Qualification indicators (failure rate) include aluminum (7.5), turbidity (5.0), chlorine dioxide (2.5), trihalomethane (2.5); there is 1 water sample with chloroform, The sum of the ratios of the actual measured concentrations of chlorodibromomethane, dichlorobromomethane and tribromoform to their respective limits reached 1.338 7, exceeding 1. Therefore, it was determined that the trihalomethane in this water sample exceeded the standard; compared with other cities, Shenzhen The concentration of disinfection by-products in municipal factory water is higher than that in other cities (during the wet season (May 26, 2008, July 14, 2009) and the dry season (December 8, 2008, 2009). On December 22, 2019, 80 factory water samples were collected from 10 municipal water plants)